The present invention generally relates to an electric motor and more particularly, to a clutch motor arrangement to be used, for example, for driving industrial sewing machines and the like, which is provided with a detection device for detecting functioning of a clutch mechanism and a control device for controlling voltages to be applied to the motor, and which is arranged to lower the impressed voltage during non-load operation of the motor to a minimum necessary value required for the motor to rotate at a speed in the vicinity of synchronous speed for reducing power consumption at the non-load operation.
Commonly, in sewing machines particularly for industrial purposes, very fast rising speeds and frequent on off functioning or inching functions are required and therefore, clutch motors employed for driving such sewing machines have considerably large power consumption, since fly wheels with a large moment of inertia are rotated at a speed close to the synchronous speed at all times, while the full power source voltage is applied to the motor even during a non-load period in which the sewing machines are not driven. Especially, in a single-phase clutch motor which occupies the majority of clutch motors, the power consumption as described above is particularly large owing to the characteristics inherent in single-phase induction motors.
Meanwhile, in the actual state of sewing work with the use of industrial sewing machines, since the working efficiency of the sewing machine is lower than 30%, the clutch motor is undesirably subjected to the non-load operation, while wasting a large amount of power for the time period more than 70%.
Conventionally, no particular countermeasures have been conceived for reduction of the power consumption during the non-load period as described above, and even if any measure is adopted, such a countermeasure has been limited only to some consideration taken during the designing of the motor main body in order to decrease the non-load loss of the motor even to a slight extent.